There were only one-third of the people who went out into the streets to celebrate Halloween this year compared to other years because the regulations became stricter, so the streets weren't as lively this year.
この場合、次のような言い方ができます。
ーThere were only one-third of the people who went out into the streets to celebrate Halloween this year compared to other years because the regulations became stricter, so the streets weren't as lively this year.
「規制が厳しくなったので、例年と比べ今年は1/3の人しか通りに出てハロウィンを祝わなかった。そのため、今年は（例年と比べ）活気がなかった」
only one-third of the people who went out で「1/3の人々しか出かけなかった」と言えます。
ご参考まで！
カナダ 
